Sandstone Types and Tectonic Settings

Understanding the origin and characteristics of different sandstone types helps match them to specific tectonic environments.

A. Mature quartz arenite: Contains abundant quartz (often >90%), well-sorted and rounded grains. This indicates significant weathering and transport, typically occurring in stable, reworking environments like shallow marine settings on passive margins.

B. Immature wacke: Characterized by a poorly sorted mixture of sand grains, rock fragments, and a significant amount of clay matrix. Angular grains suggest rapid erosion and deposition close to the source, common in tectonically active areas.

C. Feldspathic arenite: Contains a substantial amount of feldspar alongside quartz. This suggests less intense weathering or derivation from an igneous/metamorphic source area rich in feldspar, such as the uplifting blocks in a rift valley.

Matching Sandstone to Tectonic Setup

We match each sandstone type to the tectonic setting most likely to produce its characteristics:

• A. Mature quartz arenite corresponds to E. Passive continental margins. These stable margins allow for extensive reworking and weathering, leading to quartz-rich sediments.
• B. Immature wacke corresponds to F. Fore arc basins at convergent plate boundaries. These basins receive abundant, poorly sorted detritus eroded rapidly from nearby volcanic arcs.
• C. Feldspathic arenite corresponds to D. Continental rift valleys. These settings involve the uplift and erosion of continental crust, often producing feldspar-rich (arkosic) sediments.

Resulting Match

The correct matching based on geological principles is:

A - E, B - F, C - D